1. Field of the Invention
The present invention relates to transparent high impact random block copolymers compositions for use in molded and extruded articles.
2. Background of the Art
A variety of transparent thermoplastic compositions have been developed, some of which have been disclosed in the patent literature and/or introduced to the marketplace. Each of those compositions has a particular level of transparency, often characterized in terms of “haze,” which is determined in accordance with recognized test procedures. Shortcomings of those compositions include unsatisfactorily high haze values (low transparency), poor processability and poor mechanical properties, including undue hardness, low flexibility, etc. For example, previously proposed thermoplastic elastomer compositions with transparency and flexibility such as compounds based on styrene-ethylene-butadiene-styrene impact copolymers, thermoplastic vulcanized blends (TPV) or thermoplastic olefin (TPO) blends show transparency and softness levels that are still unsatisfactory in some applications.
EP 1,428,853 discloses a polypropylene polymer composition including a random propylene-alpha-olefin copolymer, the alpha-olefin being ethylene and one or more C4-C10 alpha-olefins. The polymer includes a matrix phase containing 2-12 mole % ethylene and a rubber phase containing 25-65 mole % ethylene.
EP 1,354,901 discloses a heterophasic polypropylene composition with a MFR greater than 100 g/10 min.
WO 03/106,553 discloses high impact polypropylene copolymers with matrix and rubber present in separate phases.
WO 03/046,021 discloses a polypropylene polymer composition having a MFR of from 3 to 30 g/10 min. The polymer includes 50-90% of one or more propylene copolymers having a xylene insoluble fraction of not less than 85% and 10-50% of a propylene copolymer containing 8%-40% ethylene and optionally 1-10 w-% of a C4-C8 alpha-olefin.
Other random block copolymer compositions are disclosed in EP 1,206,499, EP 373,660, EP 814,127, EP 860,457 and EP 1,162,213.
Others have attempted to make transparent compositions, but many of such compositions are problematic, particularly when attempting to make molded compositions that possess a desirable combination of properties, such as softness, flexibility and strength, while also having good processability. For example, others have been confronted with shortcomings in the area of processability, particularly for molded or extruded compositions, where the tendency of a material to crystallize quickly has enormous advantages. Many materials that have good mechanical properties lack good crystallization properties. When a composition is used for molding, it is desirable that it has a tendency to flow well and thus quickly and easily and completely fill all areas of the mold. While there is a general tendency for higher MFR materials to correspond to good flowability, a higher MFR is frequently also accompanied by an unfortunate decrease in mechanical properties; thus a higher MFR is not necessarily desirable for that reason. Furthermore, many compositions experience a trade-off in properties, e.g., where good mechanical properties may be offset by poor flexibility, e.g., undue stiffness or hardness. Accordingly, there is a need for a material that has a combination of desirable properties.
Typically, in the past one had to choose between low haze or good impact properties. The prior art does not provide a material with both low haze and good impact properties at the same time.